The influence of the renin-angiotensin system, prostaglandins (PG) and certain reflex mechanisms on the circulation is our main interest. Effects of prostaglandin synthesis inhibitors on vascular resistance and PG release in the canine renal and cutaneous vascular beds and angiotensin antagonists on vascular resistance and PG release in the renal vascular bed are being studied. Binding of angiotensin II to vascular tissue and mechanisms of its adrenergic potentiating action comprise another aspect of our work. To determine the relative pre- and postsynaptic potentiation caused by angiotensin II is our immediate goal. Recently, we found that the antihypertensive drug clonidine potentiates the chemoreceptor reflex. Studies are being done to determine the mechanism of this action. BIBLIOGRAPHIC REFERENCES: Influence of superfusion bioassay on renal effect of meclofenamate. S. Satoh and B.G. Zimmerman. Am. J. Physiol. 230:711-714, 1976. In vitro comparison of adrenergic potentiating effect of angiotensin II and des-l-aspartic angiotensin II. B. Zimmerman, M. Kuwahara and R. Harris. Fed. Proc. 35:397, 1976.